reserve m,n for Nat;
reserve i,j for Integer;
reserve S for non empty addMagma;
reserve r,r1,r2,s,s1,s2,t,t1,t2 for Element of S;
reserve G for addGroup-like non empty addMagma;
reserve e,h for Element of G;
reserve G for addGroup;
reserve f,g,h for Element of G;

theorem Th7:
  h + g = h or g + h = h implies g = 0_G
proof
  h + 0_G = h & 0_G + h = h by Def4;
  hence thesis by Th6;
end;
